The PuzzleFS container filesystem

Posted Sep 26, 2023 14:35 UTC (Tue) by hsiangkao (guest, #123981)
In reply to: The PuzzleFS container filesystem by bluca
Parent article: The PuzzleFS container filesystem

Not quite sure if I got the point. With the current upstream overlayfs, you could actually make
- EROFS + dm-verity block device blobs as data only layers;
- a small overlayfs meta layer (with EROFS + dm-verity) to merge these data storage blobs into a merged rootfs.
Thus all layers are under dm-verity protection, so the whole image won't be tampered.

Alternatively, as an EROFS self-containerd approach, EROFS could share page cache if files with same data across images without relying on overlayfs, anyway.

The PuzzleFS container filesystem

Posted Sep 26, 2023 15:57 UTC (Tue) by bluca (subscriber, #118303) [Link] (2 responses)

How would that work in practice? Say I have an erofs image with a rootfs that contains /usr/foo/a, and other two extension erofs images that contain usr/foo/b and usr/foo/c respectively. I create two overlays, each with the base, and one of the extension, so that one has usr/foo/a+usr/foo/b and the other usr/foo/a+usr/foo/c. Is memory being deduplicated, given usr/foo/a is the same?

The PuzzleFS container filesystem

Posted Sep 26, 2023 16:08 UTC (Tue) by hsiangkao (guest, #123981) [Link] (1 responses)

> I have an erofs image with a rootfs that contains /usr/foo/a, and other two extension erofs images that contain usr/foo/b and usr/foo/c respectively. I create two overlays, each with the base, and one of the extension, so that one has usr/foo/a+usr/foo/b and the other usr/foo/a+usr/foo/c. Is memory being deduplicated, given usr/foo/a is the same?

In that case, memory of /usr/foo/a is deduplicated according to how overlayfs works since /usr/foo/a is on the same EROFS instance.
That already works without any extra built-in feature.

The PuzzleFS container filesystem

Posted Sep 26, 2023 16:57 UTC (Tue) by bluca (subscriber, #118303) [Link]

Ah, that's very nice, I didn't know that, thanks!